XT, my youngest nephew, started going to school. Everyday when he arrives home, he would always showoff the stamped stars on his hands signifying that he was well-behaved or had performed good in class. And he feels sad on days that he didn't receive a star. It has been a practice in kindergarten to motivate students and reinforce good behaviors by stamping stars or giving them ribbons and the like. This practice is the application of psychological theory particularly the operant conditioning.